> Giffen goods are essential goods, such as rice, potatoes and wheat. Demand stays high when prices increase because there is no ready substitute for them.

The way Giffen goods were explained to me is that not only is there no substitute for a Giffen good, it is the substitute. Imagine you eat meat and potatoes and the price of potatoes increases. If you can no longer afford your regular diet and need to cut costs, well, meat is probably still more expensive than potatoes, so you buy less meat and even more potatoes.